Carpet and textile fibers are easily soiled and stained in everyday use. The problem of fiber soiling has become more difficult with the advent of synthetic fibers such as polypropylene, polyamide, polyethylene, and polyester, that are substantially more oleophilic (oil-loving) than traditional natural fibers such as cotton and wool.
A wide variety of materials are known to cause soiling. Soil found on fibers can include a variety of solid particles, such as fly ash or other inorganic particulates; liquids, such as oils and greases; mixtures of solids and liquids, such as soot (that contain particles mixed with oily components); and biological matter such as skin cells and sebum.
Soil typically adheres to the fiber surface by Van der Waals forces, that are effective only over very short distances. The strength of the bond depends on the forces of interaction per unit interfacial area, the area of contact, and whether a liquid is present on the fiber surface. Oily films on the fiber increase soiling. In general, the higher the viscosity of the liquid, the greater the adhesion of the liquid to the fiber. Soil particles can even adhere to initially smooth surfaces, such as polyester and polyethylene film. Soil is not commonly mechanically entrapped in the fiber.
Staining of a fiber can occur in a wide variety of ways, including through the ionic or covalent binding of an exogenous colored substance to the fiber. For example, nylon fibers are polyamides with terminal amino and carboxyl end groups. Nylon is commonly stained by acid dyes, which are colored, negatively charged molecules that ionically bind to the protonated terminal amine. Examples of staining acid dyes include liquids containing FD&C Red Dye No. 4, wine, and mustard.
For many years, soil (as opposed to stain) resistance has been imparted to carpet and textile fibers by applying a finish that repels oil and water. Perhaps the first soil resist agent for fibers was starch, that was removed along with the soil when the fiber was washed. Other water soluble polymeric stain resist finishes have included methylcellulose, hydroxypropyl starch, polyvinyl alcohol, alginic acid, hydroxyethyl cellulose and sodium carboxymethyl cellulose. As with starch, the strong disadvantage of these protective finishes is that their mechanism of action is sacrificial; they contain the soil but are removed along with it when the fiber is cleaned.
Vinyl polymers including acrylics, methacrylics and polymers of maleic acid have also been used as soil release agents. One of the first patents in this area was U.S. Pat. No. 3,377,249, issued in 1969 and assigned to Deering Milliken, disclosing and claiming emulsions of copolymers of ethyl acrylate with at least 20% acrylic, methacrylic, or itaconic acid in combination with N-methylol acrylamide.
More recently, fluorochemical soil release agents have become very popular. The fluorochemical agents are coated onto the fiber to prevent wetting of the surface by minimizing chemical contact between the surface and substances that can soil the carpet, making the substance easier to remove.
The first fluorochemical finishes focused on reducing the surface energy of the fiber to prevent the spreading of oily soils. More recently developed fluorochemical finishes have attempted to combine reduction in surface energy with hydrophilicity, as described in U.S. Pat. No. 3,728,151. Increased hydrophilicity facilitates the removal of the soil or staining material during washing. Hydrophilic moieties in soil resist finishes that include a number of hydrogen bonding groups, including polyalkylene glycols.
A number of patents describe fluorinated polymers for use as soil resist coatings for fibers, including U.S. Pat. No. 3,759,874 (describing polyurethanes that consist of a combination of an oleophilic fluorine-containing block and a hydrophilic polyethyleneoxide block) and U.S. Pat. No. 4,046,944 (describing a fluorinated condensation block copolymer, that include oleophilic fluorinated blocks and hydrophilic polyethyleneoxide blocks connected by urea linkages).
Fluorochemical coatings have been used extensively on carpet fibers, either alone (Antron Plus.TM. carpet manufactured by E. I. DuPont Nemours and Company), or in combination with an acid dye stain resistant polymeric formulation that includes a sulfonated aromatic formaldehyde condensation polymer. Examples of commercially available fluorochemical coatings for carpet fibers include Scotchgard.TM. 358 and 352 (Minnesota Mining & Mfg. Co.), Zonyl.TM. 5180 Fluorochemical dispersion, and Teflon Tuft Coat Anionic (E. I. Du Pont de Nemours and Company, Inc.). Zonyl.TM. 5180 is an aqueous fluorochemical dispersion containing a 1-10% polyfunctional perfluoroalkyl ester mixture, 10-20% polymethylmethacrylate, and 70-75% water. Teflon Toughcoat Anionic contains 5-10% perfluoroalkyl substituted urethanes, 1-5% polyfunctional perfluoroalkyl esters, and 85-90% water.
Although fluorinated finishing coats on fibers do impart an amount of soil resistance to the fiber, they all suffer from the distinct disadvantage that they are removed by routine maintenance of the fiber. None of the fluorochemical finishes available to date provides permanent protection from soiling and staining. This is a particular problem for polypropylene, that is very oleophilic, and that has begun to compete with nylon as a fiber for use in residential carpets.
Therefore, it is an object of the present invention to provide carpet and textile fiber that has permanent soil resistance.
It is another object of the present invention to provide a method of manufacture of permanently soil resistant fibers.
It is a further object of the present invention to provide a polypropylene fiber that has superior soil resistance.